Thermoplastic materials, such as hot melt adhesive, are dispensed and used in a variety of situations including the manufacture of diapers, sanitary napkins, surgical drapes as well as many others. This technology has evolved from the application of linear beads or fibers of material and other spray patterns, to air-assisted applications, such as spiral and meltblown depositions of fibrous material.
Often, the adhesive applicators will include one or more dispensing modules for applying the intended deposition pattern. Many of these modules include valve components to operate in an on/off fashion. One example of a dispensing module is disclosed in U.S. Pat. No. 6,089,413, assigned to the assignee of the present invention. This module includes valve structure which changes the module between ON and OFF conditions relative to the dispensed material. In the OFF condition, the module enters a recirculating mode. In the recirculating mode, the module redirects the pressurized adhesive material from the liquid material inlet of the module to a recirculation outlet which, for example, leads back into a supply manifold and prevents the adhesive material from stagnating. In the ON condition, the module delivers the adhesive material to a dispensing outlet for deposition on the substrate. Many other modules or valves have also been used to provide selective metering and on/off control of material deposition. For example, the known dispensing modules may be configured for contact dispensing or non-contact dispensing, such as spray dispensing, onto the target substrate to form the intended adhesive deposition pattern.
Various dies or applicators have also been developed to provide the user with some flexibility in dispensing material from a series of dispensing modules. For short pattern lengths, only a few dispensing modules are mounted to an integral manifold block. Longer applicators may be assembled by adding additional modules to the manifold. Additional flexibility may be provided by using different die tips or nozzles on the modules to permit a variety of deposition patterns across the applicator as well. The most common types of air-assisted dies or nozzles include meltblowing dies, spiral nozzles, and spray nozzles. Pressurized air used to either draw down or attenuate the fiber diameter in a meltblowing application, or to produce a particular deposition pattern, is referred to as process air. When using hot melt adhesives, or other heated thermoplastic materials, the process air is typically also heated so that the process air does not substantially cool the thermoplastic adhesive material prior to deposition of the adhesive material on the substrate or carrier. Therefore, the manifold or manifolds used conventionally to direct both adhesive material and process air to the module include heating devices for bringing both the thermoplastic material and process air to an appropriate application temperature.
In addition, it is also known that some articles of manufacture benefit from the use of reduced amounts of adhesive applied along certain portions of a deposition pattern. In order to achieve this varying amount of adhesive, multiple pumps and multiple valves are provided to feed a single dispensing outlet in the dispensing module (or two dispensing outlets configured to apply adhesive on the same portion of the substrate). One example of this type of system is disclosed in U.S. Patent Publication No. 2013/0274700, which is assigned to the assignee of the present invention. Such a system enables predictable variations in flow along a machine direction to thereby use reduced amounts of adhesive when these types of patterns are beneficial.
Despite these various improvements, it would be desirable to further enhance the operational functionality and efficiency of applicators for dispensing adhesive in various adhesive deposition patterns. To this end, it would be desirable to enable near-instantaneous modification of adhesive output volume without requiring duplicative valve and pump structures that can add to manufacturing costs and maintenance requirements for an applicator. Furthermore, it would be desirable to provide further adjustable control of the amount of reduction of adhesive flow when switching between partial volume flow and full volume flow in these dispensing applications, and particularly without using complex variable pump devices and control systems.